In the prior art, a rotation sensor is used to detect the rotational speed of a vehicle wheel or power transmission shaft. The rotation sensor has a sensor portion, a wire for transmitting electrical signals output from the sensor portion, and a resin housing covering the sensor portion and the wire. The wire, which is connected to the sensor portion inside the housing, extends outward from the housing. The rotation sensor is normally used under severe conditions and is thus required to have a high water resistant property. Patent document 1 and patent document 2 both disclose a sealing structure for preventing water leakage through the interface between the housing and the wire.
In patent document 1, a wire (more specifically, the sheath covering a conductive line) and a housing are made of the same material. When molding the housing, the housing and the wire are fused to each other to improve the sealing. More specifically, the housing is formed by pouring a molten resin material into a housing formation mold in a state in which the sensor portion and an end of the wire is arranged in the mold. The heat from the molten resin material poured into the mold fuses the resin material with the wire.
The mold includes a gate for injection of the molten resin material into the mold. However, depending on the shape of the molded housing, the injection gate is distant from the wire, which is arranged in the mold. In this case, the temperature of the molten resin material injected into the mold through the gate may decrease before the molten resin material reaches the wire. Thus, the surface temperature of the wire may not rise sufficiently. This would lower the adhesive strength between the wire and the resin material of the housing and cause the sealing at the interface between the housing and the wire to be insufficient.
In patent document 2, a housing formation mold includes a constricting portion, which is located where the wire is arranged. The constricting portion is formed by reducing the diameter of an inner wall surface of the mold at the location where the wire is arranged. The distance between the wire and the inner wall surface of the mold is reduced by the constricting portion. When filling the mold with a molten resin material, the constricting portion presses the molten resin material against the wire. This efficiently transfers the heat of the molten resin material to the wire and fuses the wire to the resin material of the housing in an optimal manner.
However, in patent document 2, the constricting portion must be formed at the location where the wire is arranged. This limits the shape of the housing. That is, the constricting portion must be taken into consideration when determining the shape of the housing. This makes it difficult to reduce the size of the housing and to shape the housing in accordance with the location at which the rotation sensor is installed.
Patent Document 1: Japanese Laid-Open Patent Publication No. 10-115629
Patent Document 2: Japanese Laid-Open Patent Publication NO. 2000-19185